1. Field of the Invention
The present invention relates generally to pulsed signal circuitry and, more particularly, to a circuitry for the generation and synchronous detection of optical pulsed signals contaminated by a large additive background noise characterized by a high inherent signal-to-noise ratio.
2. The Prior Art
Various types of spectrometers have been used over the past several decades for the spectrochemical analysis of unknown elements in a sample solution. For instance, in an atomic absorption spectrometer, an excitation source such as a hollow cathode lamp is employed to excite the sample atoms. The spectrometer then measures the radiation absorbed by these sample atoms so as to determine their concentration within the sample. In atomic and fluorescent emission spectrometers, it is the intensity of the emitted characteristic radiation that is measured and related to the concentration of the particular element in the sample. All of these, as well as others, such as spark-gap spectrometers encounter a problem of noise contamination. This problem of noise contamination is particularly acute when analyzing a sample containing a plurality of unknown elements. The problem is further complicated in atomic fluorescence spectroscopy by the fact that unwanted thermally excited emission also occurs at the same wavelength as fluorescent emission.
Additive noise contamination is essentially of two kinds:
(a) noise characterized by having a relatively constant value over a wide range of frequencies, known as white-frequency spectrum noise, and (b) noise whose value changes inversely with frequency, known as excess low frequency noise since it primarily occurs at the lower end of the frequency spectrum, and is also referred to as 1/f frequency spectrum noise.
In order to have a reliable, accurate spectrometer with an acceptable detection limit, the spectrometer must have a good output signal-to-noise ratio. In order to achieve such a good output signal-to-noise ratio, most if not all noise contamination (i.e., extraneous noise) must be eliminated from the desired signal. Furthermore, the manner employed to eliminate the extraneous noise should be simple, reliable and having a useful life at least coterminous with that of the spectrometer in which it is incorporated. Thus, extraneous noise elimination involves difficult complexities. Since elimination of the noise at the source is seldom if ever possible, some kind of signal processing that reduces the extraneous noise is needed. Presently available techniques at noise attenuation have been wanting for either not doing an adequate job or being too cumbersome, hence expensive. Thus, there is a need for a fresh approach to eliminate extraneous noise when working with pulse type signals.